In order to fix bug 1935076, we'll have to add a pure js fallback in case wasm is disabled
or simd isn't supported. Unfortunately, this fallback will take some space.
So, the main goal of this patch is to reduce the overall size (by ~93k).
As a side effect, it should make easier to use an other wasm file (which must export
_jp2_decode, _malloc and _free).
- Over time the number and size of these factories have increased, especially the `DOMFilterFactory` class, and this split should thus aid readability/maintainability of the code.
- By introducing a couple of new import maps we can avoid bundling the `DOMCMapReaderFactory`/`DOMStandardFontDataFactory` classes in the Firefox PDF Viewer, since they are dead code there given that worker-thread fetching is always being used.
- This patch has been successfully tested, by running `$ ./mach test toolkit/components/pdfjs/`, in a local Firefox artifact-build.
*Note:* This patch reduces the size of the `gulp mozcentral` output by `1.3` kilo-bytes, which isn't a lot but still cannot hurt.
*Please note:* This removes top level await from the GENERIC builds of the PDF.js library.
Despite top level await being supported in all modern browsers/environments, note [the MDN compatibility data](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await#browser_compatibility), it seems that many frameworks and build-tools unfortunately have trouble with it.
Hence, in order to reduce the influx of support requests regarding top level await it thus seems that we'll have to try and fix this.
Given that top level await is only needed for Node.js environments, to load packages/polyfills, we re-factor things to limit the asynchronicity to that environment.
The "best" solution, with the least likelihood of causing future problems, would probably be to await the load of Node.js packages/polyfills e.g. at the top of the `getDocument`-function. Unfortunately that doesn't work though, since that's a *synchronous* function that we cannot change without breaking "the world".
Hence we instead await the load of Node.js packages/polyfills together with the `PDFWorker` initialization, since that's the *first point* of asynchronicity during initialization/loading of a PDF document. The reason that this works is that the Node.js packages/polyfills are only needed during fetching of the PDF document respectively during rendering, neither of which can happen *until* the worker has been initialized.
Hopefully this won't cause any future problems, since looking at the history of the PDF.js project I don't believe that we've (thus far) ever needed a Node.js dependency at an earlier point.
This new pattern for accessing Node.js packages/polyfills will also require some care during development *and* importantly reviewing, to ensure that no new top level await is added in the main code-base.
*Please note:* These changes only affect the GENERIC build, since `NullL10n` is only a stub elsewhere (see PR 17135).
After the changes in PR 17115, which modernized and improved l10n-handling, the `NullL10n`-implementation is no longer a good fallback for the "proper" `L10n`-classes.
To improve this situation, especially for the *standalone* viewer-components, this patch makes the following changes:
- Let the `NullL10n`-implementation extend an actual `L10n`-class, which is constant and lazily initialized, to ensure that it works *exactly* like the "proper" ones.
- Automatically bundle the "en-US" l10n-strings in the build, via the pre-processor, such that we don't need to remember to manually update them.
- Ensure that the *standalone* viewer-components register their DOM-elements for translation, similar to the default viewer, since this will allow future code improvements by using "data-l10n-id"/"data-l10n-args" in most (if not all) parts of the viewer.
- Remove the `NullL10n` from the `AnnotationLayer`, to avoid affecting bundle size too much.
For third-party users that access the `AnnotationLayer`, as exposed in the main PDF.js library, they'll now need to *manually* register it for translation. (However, the *standalone* viewer-components still works given the point above.)
This has been deprecated since version `2.15.349`, which is a year ago.
Removing this will also simplify some upcoming changes, specifically outputting of JavaScript modules in the builds.
By leveraging import maps we can get rid of *most* of the remaining `require`-calls in the `src/display/`-folder, since we should strive to use modern `import`-statements wherever possible.
The only remaining cases are Node.js-specific dependencies, since those seem very difficult to convert unless we start producing a bundle *specifically* for Node.js environments.
